Jab,
Thanks for the query. I made as few assumptions based on "M"'s original mission profile of 750NM and having flown both powerplants, I assumed the PT-6 powered single would not be run continuously at high speed cruise for the purposes of reliability, overall economy and optimised maintenance accruals. Whereas the AC695B at altitude, cruises at a genuine 302 KTAS regardless (near the same speed as a King Air 350).
Assuming the mission is run fairly frequently (a couple of times each week) the AC695B would take 2.48 hours flight time for a 187.5 USG fuel burn and the PC-12 would take 2.88 flight hours (@260KTAS) and burn approximately 156 USG. And yes the single will burn 20 percent less fuel per sector than the legacy twin.
However, depending on the payload the AC 695B might regularly be able to take return fuel (design range with 7 passengers 1,400NM) and the PC 12 might need a fuel top up at the out port differential fuel price (design range with 3 passengers 1573NM). Outport differential fuel prices at non Capital City locations (if that is where "M"'s mission flies to) makes fuel expensive to purchase and needs to be considered.
The cost of fuel differential pricing, together with the 0.40 flight hours saving per sector at 3 missions per week for 48 weeks (allowing for an annual holiday) results in the AC965B using 115.5 less airframe and engine propeller maintenance hours overall per year than the PC-12. All of which combined makes for a compelling argument favouring the Commander over the Pilatus.
You could of course shave the PC-12 flight hour margins by running the PT-6 'flat out', but the increased fuel costs at the out port from continuous high speed cruise, combined with the almost inevitably increasing maintenance burden on the PT-6 powerplant, would tip the balance further towards the AC695B.
Considering the distances involved I do think a small jet would provide a more cost effective answer to "M"'s mision requirement.
Jets burn more fuel than turboprops, however the overall maintenance burden, en-route charges, etc. with a small jet would be less over a 750NM sector and if the mission did fly the 3 returns per week that I have assumed, at the end of the year the overall costs of running a jet compared with a turboprop might prove to be less.
A small jet such as a Raytheon Premier 1A (single pilot and 7 passengers) at high speed cruise (450KTAS) would flying the 750 NM mission 3 times each week for 48 weeks in the year for 235 less flight hours than the AC695B and although the jet's fuel burn is greater (approximately 225 USG for the sector) there might be a substantial cost saving overall due to the reduced flight hours, etc..
The Oracle